Performance of multicarrier CDMA with DPSK modulation anddifferential detection in fading multipath channels

Multicarrier (MC) direct sequence (DS) code division multiple access (CDMA) with differential phase-shift keying (DPSK) modulation and differential detection is proposed. Transmitted data bits are differentially encoded after serial-to-parallel conversion to a number of parallel streams. On each branch, encoded bits are direct sequence spread spectrum (SS) modulated and transmitted using different carriers. The system is analyzed with a differential detector in static Rayleigh fading multipath channel, in fast Rayleigh fading multipath channel and for variable overlapping between carrier spectra in static fading channel. Closed-form expressions are derived for the error probability and evaluated for many cases. The performance is compared to that of a system using phase-shift keying (PSK) with conventional matched filter (CMF) coherent receiver. For static fading channel, the error probability performance of the differential detector is close to that of CMF receiver. For fast fading, the performance degrades slightly with increasing fading rate. Finally; successive carriers of the system are allowed to overlap with various overlapping percentages. The condition of a single path can be achieved by increasing both the number of carriers and the separation between successive carriers. Also, for each number of carriers, there exists an optimum overlapping percentage at which the system performance is optimized. The performance of the proposed DPSK with differential detection system is close to that of PSK with CMF receiver, but the former is simpler to implement     

Microcellular direct-sequence spread-spectrum radio system usingN-path RAKE receiver

A microcellular local area network (LAN) for indoor communications is proposed using code-division multiple access (CDMA) and differential phase-shift keying (DPSK) for data modulation. The pseudonoise (PN) codes in the transmitters of the base station are mutually synchronized. For this purpose, sets of Gold code sequences having low cross correlation have been found by an exhaustive computer search. Together with wideband measurements of the indoor radio channel at 900 MHz, a five-path RAKE receiver was designed to combat fading effects and to process the time diversity by using multipath signal reception. Each receiver path is demodulated independently. Several methods of diversity combining of these paths have been investigated. Acquisition and tracking of the spreading code in the receiver are controlled by a digital signal processor (DSP). Experimental results of the CDMA system are presented, showing the behavior in a multipath environment     

PN code synchronization effects on narrow-band interferencerejection in a direct-sequence spread-spectrum receiver

The impact of imperfect synchronization on the performance of prediction-error interference rejection filters in noncoherent direct-sequence (DS) spread-spectrum communications is considered. Bit-error-rate analysis (BER) analysis (BER) of binary DPSK (differential phase-shift keying) data modulation used in conjunction with direct-sequence spread-spectrum is used as a performance measure. A first-order noncoherent delay-lock loop is used for the pseudonoise (PN) code tracking. Conditional BER results for the DS/DPSK systems for fixed values of the code tracking error are obtained. The average BER of the system is then evaluated by averaging the conditional BER expressions over the probability density function of the code tracking error. Results include the effects of both a single fading tone and a narrowband Gaussian interferer on the overall system performance. Interferer offset frequency is considered in determining the code tracking loop noise as well as the receiver BER     

Hybrid DS/SFH spread-spectrum multiple access with predetectiondiversity and coding for indoor radio

The authors derive close upper and lower bounds on the average bit error probability for hybrid direct-sequence/slow-frequency-hopped spread-spectrum multiple-access (DS/SFH-SSMA) systems with noncoherent DPSK demodulation, using predetection diversity (selection combining and equal gain combining) in conjunction with interleaved channel coding (Hamming (7,4) code and BCH (15,7) code) operating through indoor radio channels. A multipath Rayleigh fading model is assumed for the indoor radio channel. The results show that the DS portion of the modulation combats the multipath interference, whereas the FH portion is a protection against large multiaccess interference. It is shown that, for the considered types of channel coding, the use of predetection diversity is still essential for obtaining satisfactory error performance     

Joint noncoherent demodulation and decoding for the block fading channel: a practical framework for approaching Shannon capacity

The paper contains a systematic investigation of practical coding strategies for noncoherent communication over fading channels, guided by explicit comparisons with information-theoretic benchmarks. Noncoherent reception is interpreted as joint data and channel estimation, assuming that the channel is time varying and a priori unknown. We consider iterative decoding for a serial concatenation of a standard binary outer channel code with an inner modulation code amenable to noncoherent detection. For an information rate of about 1/2 bit per channel use, the proposed scheme, using a quaternary phase-shift keying (QPSK) alphabet, provides performance within 1.6-1.7 dB of Shannon capacity for the block fading channel, and is about 2.5-3 dB superior to standard differential demodulation in conjunction with an outer channel code. We also provide capacity computations for noncoherent communication using standard phase-shift keying (PSK) and quadrature amplitude modulation (QAM) alphabets; comparing these with the capacity with unconstrained input provides guidance as to the choice of constellation as a function of the signal-to-noise ratio. These results imply that QPSK suffices to approach the unconstrained capacity for the relatively low information and fading rates considered in our performance evaluations, but that QAM is superior to PSK for higher information or fading rates, motivating further research into efficient noncoherent coded modulation with QAM alphabets.     

Data-aided linear prediction receiver for coherent DPSK and CPMtransmitted over Rayleigh flat-fading channels

In this paper, a new data-aided linear prediction receiver for coherent differentially encoded phase-shift keying (DPSK) and coherent continuous phase modulation (CPM) over Rayleigh flat-fading channels is presented, This receiver uses the previously detected symbols to estimate the carrier-phase reference and predict the channel gain continuously and therefore makes the optimal coherent detection of DPSK and CPM. The receiver has a simple structure and can be implemented easily. This is due partly to the fact that the linear predictors used for channel estimation do not depend on the autocorrelation function of the fading process. Simulation results on the bit error performance of QDPSK and minimum-shift keying (MSK) with the new receiver are given for both the additive white Gaussian noise (AWGN) and the Rayleigh flat-fading channels. The results show that the proposed receiver provides almost the same bit error rate (BER) performance as the ideal coherent receiver in an AWGN channel, is very robust against large carrier frequency offset between transmitter and receiver, and can provide a reasonably good BER performance in a fast Rayleigh fading channel. Finally, a multisample receiver is discussed and its error rate performance is evaluated by means of computer simulations. The results show that the multisample receiver provides good BER performance for higher fading rate     

Differential unitary space-time modulation

We present a framework for differential modulation with multiple antennas across a continuously fading channel, where neither the transmitter nor the receiver knows the fading coefficients. The framework can be seen as a natural extension of standard differential phase-shift keying commonly used in single-antenna unknown-channel systems. We show how our differential framework links the unknown-channel system with a known-channel system, and we develop performance design criteria. As a special ease, we introduce a class of diagonal signals where only one antenna is active at any time, and demonstrate how these signals may be used to achieve full transmitter diversity and low probability of error     

一种用于DS扩频信号非相干检测的差分延迟SAW相关器

本文介绍了用于ＤＰＳＫ调制的ＤＳ扩频信号非相干检测的一种ＳＡＷ器件的设计方法。对所研究的差分延迟功能均集于单一器件中。因为没有采用独立的延迟线，故消除了带限影响，ＤＰＳＫ解调器延迟支路无插入损耗。     

Theoretical investigation of optical wavelength conversion techniques for DPSK Modulation formats using FWM in SOAs and frequency comb in 10 gb/s transmission systems

We have investigated the wavelength conversion techniques for differential phase-shift keying (DPSK) modulation formats in 10 Gb/s transmission systems, compared with the non-return-to-zero (NRZ) modulation format. For the wavelength conversion of DPSK modulation formats, we employed the wavelength converters based on the four-wave mixing (FWM) in semiconductor optical amplifiers (SOAs) and the frequency comb generated by phase modulation. The power penalty at 10/sup -9/ bit error rate was used as a measure of the system performance degraded by the wavelength conversion. Our simulation results show that the DPSK modulation formats have a smaller power penalty than the NRZ modulation format for the wavelength conversion using the FWM effect in an SOA due to a much lower pattern effect. However, as the wavelength conversion uses the frequency comb generated by phase modulation, it has a similar power penalty compared with the NRZ modulation format. It is also shown that the DPSK modulation formats are possible to obtain the power penalty less than 0.4 dB for both wavelength conversion techniques.     

Comparison of DPSK and MSK bit error rates for K andRayleigh-lognormal fading distributions

The composite Rayleigh-lognormal distribution is mathematically intractable for the analytical evaluation of such a communication system performance metric as bit error rate. The composite K distribution closely approximates the Rayleigh-lognormal and is potentially useful for analytical manipulations. In this contribution we derive the bit error rates of differential phase-shift keying (DPSK) and minimum shift keying (MSK), in manageable closed forms, for the K distribution model of multipath fading and shadow fading, and show, numerically, the close agreement between these results and those based on the Rayleigh-lognormal distribution     

Differential Phase-Shift Keying Performance on L-Band Aeronautical Satellite Channels: Test Results and a Coding Evaluation

The problem of communicating binary information from ground to aircraft viaL-band aeronautical satellite channels is addressed, with particular attention given to the effect of and means of combating diffuse-scattered multipath interference. Differential phase-shift keying (DPSK) is considered throughout. Test results of a recent flight-test program are summarized and compared to theory for uncoded DPSK. We then discuss and evaluate the use of diffuse convolutional codes in conjunction with threshold decoding to improve error probability on the fading channel. Simulation has shown that a power saving of 8 dB may be gained at 10^-5error rate for typical channel conditions with very little complexity.     

Essence and Advantages of FM-DCSK Versus Conventional Spread-Spectrum Communication Methods

Frequency-modulated differential chaos shift keying (FM-DCSK) is essentially a technique that combines modulation with a spread-spectrum property for communications. It is also an effective technique similar to recent multiantenna methodologies that can make use of multipath effects, thereby achieving an excellent anti-multipath fading capability. Through analysis and simulation, this paper reports some essential characteristics and advantages in the system performance of the newly proposed M-ary FM-DCSK technology. The basic design of the M-ary FM-DCSK-based chaotic spread-spectrum communication system and a comparison with its conventional equivalent are presented. It is shown that the former is not only robust in multipath fading environments and simple in implementation, but also flexible in adjusting system parameters and trading-off several effects among bandwidth efficiency, energy efficiency, data rate, and error performance. It is demonstrated that the FM-DCSK technique is promising for the next generation of wireless communication systems as an excellent modulation and spread-spectrum scheme candidate.     

A systematic approach to the design and analysis of optimum DPSKreceivers for generalized diversity communications over Rayleigh fadingchannels

A generalized diversity channel is introduced that models a variety of wireless communication systems that use time, frequency, multipath, and/or antenna diversity with various interbranch correlations between signaling waveforms and the fading and additive noise processes. In the context of this general model, a systematic approach to the design and analysis of optimum noncoherent differential phase-shift keying (DPSK) receivers is introduced. In particular, it is shown how the minimum error probability (MEP) and the generalized likelihood ratio tests (GLRT) can be applied to obtain optimal noncoherent combining rules. A comparative error-rate analysis of the GLRT and MEP detectors and an ad hoc equal-gain combiner is provided for binary signaling, and the suitability of the three schemes is determined as a function of fading characteristics. The asymptotic bit-error-rate analysis is undertaken for the MEP detector for slow and fast fading channels. An estimator-detector decomposition of the noncoherent MEP rule is obtained which allows an insightful comparative study of the fundamental limits of binary phase-shift keying and DPSK modulation-detection methods for both slow and fast fading. The results of this paper are also applicable to postdecorrelative receivers in multiuser channels     

Space-time overlays for convolutionally coded systems

We consider the design of space-time overlays to upgrade single-antenna wireless communication systems to accommodate multiple transmit antennas efficiently. We define the overlay constraint such that the signal transmitted from the first antenna in the upgraded system is the same as that in the single-antenna system. The signals transmitted from the remaining antennas are designed according to space-time coding principles to achieve full spatial diversity in quasi-static flat fading channels. For both binary phase-shift keying (BPSK) and quaternary phase-shift keying modulation systems, we develop an algebraic design framework that exploits the structure of existing single-dimensional convolutional codes in designing overlays that achieve full spatial diversity with minimum additional decoding complexity at the receiver. We also investigate a concatenated coding approach for a BPSK overlay design in which the inner code is an orthogonal block code. This approach is shown to yield near optimal asymptotic performance for quasi-static fading channels. We conclude by offering a brief discussion outlining the extension of the proposed techniques to time-varying block fading channels.     

Robust channel estimation for OFDM systems with rapid dispersivefading channels

Orthogonal frequency-division multiplexing (OFDM) modulation is a promising technique for achieving the high bit rates required for a wireless multimedia service. Without channel estimation and tracking, OFDM systems have to use differential phase-shift keying (DPSK), which has a 3-dB signal-to-noise ratio (SNR) loss compared with coherent phase-shift keying (PSK). To improve the performance of OFDM systems by using coherent PSK, we investigate robust channel estimation for OFDM systems. We derive a minimum mean-square-error (MMSE) channel estimator, which makes full use of the time- and frequency-domain correlations of the frequency response of time-varying dispersive fading channels. Since the channel statistics are usually unknown, we also analyze the mismatch of the estimator-to-channel statistics and propose a robust channel estimator that is insensitive to the channel statistics. The robust channel estimator can significantly improve the performance of OFDM systems in a rapid dispersive fading channel     

Impact of laser phase noise on the performance of a {3×3}phase and polarization diversity optical homodyne DPSK receiver

An analysis of the impact of laser phase noise on the performance of a {3×3} phase- and polarization-diversity differential phase-shift keying (DPSK) receiver is done for the phase and shot-noise limited case. The results show that, for zero laser linewidths, the maximal signal power penalty of the {3×3} phase- and polarization-diversity DPSK receiver with respect to the conventional heterodyne DPSK receiver is approximately 0.7 dB for P_e =10^-9. For nonzero laser linewidths, it appears that, depending on the laser linewidth, for large signal-to-noise ratios the performance of the analyzed {3×3} phase- and polarization-diversity DPSK receiver is close to that of the ideal conventional heterodyne DPSK receiver. For a rectangular intermediate-frequency filter, the maximum allowable normalized laser linewidth (Δυ×T) for the (3×3) phase and polarization diversity DPSK receiver is found to be approximately 0.46% for a power penalty of 1 dB     

Differential Phase-Shift Keying Performance Under Time-Selective Multipath Fading

Differential phase-shift keying (DPSK) performance analysis in the presence of multipath is extended to include cases in which the Doppler spread is on the order of the bit rate or greater. As the Doppler spread is increased from zero, the performance degrades below that predicted by Jones [1]. However, as the Doppler spread is increased beyond values on the order of the bit rate, performance improves. In the limit as the Doppler spread approaches infinity, with total multipath power held constant, performance approaches that of ideal DPSK as expected. Bit error rate performance in the presence of time-selective Rician fading is presented along with confirming experimental data obtained with a channel simulator.     

Reduction of AM-induced penalty in DPSK receivers by sum-squaredemodulation

A DPSK (differential phase shift keying) demodulator which is insensitive to the amplitude modulation induced by semiconductor optical amplifier phase modulators is proposed. The demodulator consists of only two additional power dividers/combiners, compared to a traditional DPSK demodulator. Analysis shows that the receiver penalty caused by amplitude modulation can be reduced from 2-4 dB to zero. The demodulator is demonstrated in a 2.5-Gb/s DPSK system experiment using an optical amplifier as phase modulator     

The Distribution of Error Probability for Rayleigh Fading and Gaussian Noise

The distribution function of the probability of error in the presence of Rayleigh fading and Gaussian noise is determined for the basic binary modulation schemes of coherent frequencyshift keying (CFSK), noncoherent frequency-shift keying (NCFSK), differential phase-shift keying (DPSK), and coherent phase-shift keying (CPSK). General expressions for the distribution function of error probability are also derived when linear maximal-ratio diversity combining is employed. Results are given for various values of average error probability and various orders of diversity.     

Phase-Tunable Low-Loss, S-, C-, and L-Band DPSK and DQPSK Demodulator

Differential phase-shift keying (DPSK) and differential quadrature phase-shift keying (DQPSK) are touted as performers and reliable advanced modulation formats for next-generation optical transmission systems. One key device enabling such systems is the delay interferometer, converting the signal phase information into intensity modulation to be detected by the photodiodes. We developed an all-fiber delay-line interferometer for DPSK and DQPSK demodulation in the S-, C-, and L-band with low insertion loss, low-birefringence, and greater than 30 dB of extinction ratio over 100 nm and 20 dB from 1460 to 1640 nm in a single device. The device also features insensitivity to mechanical vibration, very low port imbalance (0.1 dB), and very low time delay between all outputs (0.1 ps). The device is highly reliable with a demonstrated failure-in-time rate of less than 100.